In the past, steam injection elements have been employed to heat water in a heating chamber by injecting steam into the water. A typical prior art steam injection water heater is disclosed in U.S. Pat. No. 2,455,498 to C. T. Kern. These heaters worked satisfactorily at relatively low steam pressures, e.g., below 300 psi. At high steam pressures, water hammer develops in the system, presumably due to sudden collapse of relatively large steam bubbles which are created by the high pressure steam, as the steam condenses in the water. The orifices in the foraminous steam injection element were made smaller in an attempt to eliminate the water hammer, but it persisted, notwithstanding substantial reduction in orifice size. Moreover, there is a limit to reduction in the size of the orifices, since they must inject a sufficient volume of steam into the water to heat it to the desired temperature.